Automatic telephone system



April l4, 1942. N. H. sAuNDERs 2,279,531 AUTQMATIG'TELEPHONE SYSTEM 4 Filed July 18,` 1940 2 sheets-sheet 1 Narman/'zzhiers April 14, 1942. N. H. sAuNDERs AUTOMATIC TLEPHONE SYSTEM -2`sheets-sheet yaf Patented Apr. 14, 1942 AUTOMATIC TELEPHONE SYSTEM Norman H. Saunders, Chicago, Ill., assignor to Kellogg Switchboard and Supply Company,v Chicago, Ill., a corporation of Illinols Application July 18, 1940, Serial No. 346,069

24 Claims.

The present invention relates in general to automatic telephone systems, in which connections are established by automatic switches under control of a dial or calling device at the calling subscribers station. The switches employed in such systems are of several types, depending on the functions they are intended to perform. Thus systems in common use may include finder switches, selector switches, and connector switches.

The invention relates more in particular to selector switches. These switches are provided on a percentage basis. When a subscriber makes a call his line is extended to an idle selector switch by a preliminary trunking operation, performed by a finder switch, for example, after which the selector switch is directively controlled by the dial to select a main group of trunk lines leading to connector switches or to a second order of selector switches, depending on the size of the system. Upon the completion of the directive control, the selector switch operates automatically to select an idle trunk line in the selected group and to extend the calling subscribers line to such trunk line.

The object of the invention is to produce a new and improved selector switch of the foregoing character, adapted for use either as a rst selector or a second selector, or in any position in an automatic switch train where selectors are customarily used.

A special object of the invention is to provide a new and improved selector switch of therelay type, that is, a selector switch in which all the various functions of the switch are performed by relays.

The invention and the features of improvement included therein will be described fully hereinafter with reference to the accompanying drawings, Figs. 1 and 2, which show diagrammatically the relays and circuit connections of a complete selector switch, together with the circuit connections whereby the selector is made available to a calling line to perform the functions of a rst selector.

Referring to the drawings, the reference char acter A indicates a subscribers station of known type, including a transmitter I, receiver 2, and the usual dial or calling device 3. The station A is connected with the exchange over a pair of line conductors ID and II, which terminate in the usual line circuit, represented by the rectangle I5. Conductors II, I2, and I3 are the socalled normal conductors, which extend to the connectors which have access to the line of station A.

It may be assumed that finder switches of the relay type are used for connecting with calling lines and extending them to first selector switches. The relays 2l] and 2l are tens and units relays of such a finder switch. Each relay has a plurality of sets of contacts, although the drawing shows only the single contact set on each relay which is involved in extending the line of station A. The rectangle I6 represents a group of control relays for the finder switch, including a relay allotter which assigns idle selectors for use by calling lines.

The conductors 22-25 are the conductors of a trunk line extending to a first selector switch. Conductors 22 and 23 are the line conductors, conductor 24 is the test conductor, while con.- ductor 25 is the holding conductor.

The selector switch is shown in the remainder of Fig. 1 and in Fig. 2. Relays 26 to 35, inclusive, Fig. 1, are the selector control relays. Relays IIlI to IIB, inclusive, of which only the first two and last two are shown, are so-called counting relays, which perform a numerical group selection in response to the dialling of a digit at the calling station, and which also function as searching relays to select an idle trunk. Relays III and II2 are additional searching relays, which provide for'twelve trunks in each group instead of ten. Relay II3 is an overflow relay, which` is energized in case all the trunks in a selected group are found busy.

The selector switch may have access tot ten groups of trunk lines, and for that purpose may be provided with ten group relays each having suiiicient sets of contacts for connecting up all the trunksof a group. However, at the first selectors it is the usual practice to omit the first group of trunk lines, as there is danger of false selection of the first group by an accidental preliminary impulse; and accordingly it will be assumed that the selector shown has access to only nine groups of trunk lines and is provided with nine group relays. Of these nine group relays the second and tenth group relays are shown in the drawing, being indicated by reference numerals |22 and |20, respectively.

The drawings show the last two trunk lines in the second group and the corresponding trunks in the tenth group. More specifically, conductors I2I, |22, and I23 are the conductors of the twelfth trunk line in the second group, while conductors |24, |25, and |26 are the conductors ofthe eleventh trunk line of the second group.

Conductors |21, |28, and |29 are the conductors of the twelfth trunk line of the tenth group, while conductors |33, |3|, and |32 are the conductors of the eleventh trunk line of the tenth group. Each group relay, of course, has ten contact sets in addition to the two sets shown, to take care of trunks one to ten, but these additional contact sets have been omitted for lack of space. The trunk lines are multipled to other selectors, as indicated in the drawings.

The selector switch is not limited to use as a iirst selector, as shown herein, but may also lbe used as a second or third selector` without change, except that the holding conductor is omitted. The holding conductors are used only on first selectors and not only serve to maintain the nder connecting relays in operated position, but also function as auxiliary test conductors -over which the idle or busy condition of the selectors is manifested to the allotter heretofore mentioned. When used as a second selector, the selector disclosed herein is tested over the usual test conductor corresponding to conductor 24, an'd a busy key BK is provided for lmaking the selector artificially busy to incoming calls.

This key is not required on first selectors and maybe omitted if desired. The first selectors are articially busied at the allotter.

The operation of the selector switch 4will now be described. When the subscriber at station A removes the receiver from the hook, a bridge is closed across the line Vconductors IHl and |Y| and the subscribers line relay (part of the 1line circuit) is operated in the usual manner. Gn energizing, the line relay causes the operation of a finder switch associated with an idle selector switch to extend the subscribers line to such selector switch. Assuming that the selector switch shown is idle at the time, vand has been allotted for use on the next call, the tens and units relays 2|) and 2| of the associated finder are energized, and the lineconductors Hl and are extended by way of conductors |1 and |8 and contacts of relays 2E! and 21|, to the trunk conductors 22 and 23.

The line relay 21 of the selector is now Lenergized over the calling line `in the usual manner, and at contact 4| closes a circuit for the slow acting release relay 23. On energizing, the latter relay prepares an impulsing circuit at contact 44, grounds the test conductor 24 at contact 42, and grounds the holding conductor -25 at contact 45.

.The grounding of holding conductor 255 establishes holding circuits for the tens and units relays 20 and 2| in the finder switch, which maintain these relays energized after the control apparatus has restored. The grounding of the test conductor 24 energizes the cut-ofi' relay in the line circuit, which disconnects the line relay lfrom the subscribers line and allows it to restore. Ground potential is also placed on conductor |4, whereby the subscribers Vline is made busy to the connectorswitches which have access to it.

These operations are all well known and require no detailed explanation.

Returning to the selector switch, energization of the release relay 28 closes a circuit for relay 34, extending from ground by way of contact 45, conductor 1|, contact |41, chain Contact |49 on ,group relay |20, and similar contacts including -contact 15|! on other group relays,chain contacts |40 to |45, inclusive, contact :58, and windingfof relay 34 to battery. On energizing, relay `34 prepares the group relay marking .circuit at contact 65 and prepares a locking circuit for itself at contact 64.

The energization of release relay 28 also brings about the energization of the slow acting changeover relay 29, over a circuit extending from ground by way of contact 42, contact 38, conductor 10, busy key BK, conductor 18, contact |53, conductor 19, contact 69, and lower winding of relay 29 to battery. On energizing, relay 29 opens a point in the group relay marking circuit at contact 49, prepares a holding circuit for itself at contact 4B, prepares the counting relay control circuits at contact 41, and at contact 46 connects dial tone to one side of the calling line. The signal thus transmitted over the line informs the calling subscriber that the dialling of the number of the called line may proceed.

'It' will be assumed that the first digit of the number is the digit 0. When the calling device is operated in accordance with this digit, ten momentary interruptions are produced in the sub-station bridge across the calling line and Ithe line relay is caused to deenergize lten times in rapid succession. These operations of. the line relay'control the counting relays ml to ||t0, inclusive, as will be described. It may be mentioned liii-st, however, that the .release relay 2B,

rbeing slow to deenergize, does not fallback in response to the momentary interruptions of rits circuit during the deenergizations of the 'line When the line relay 21 falls back in response to the first interruption Vof the line circuit, it transmits yan impulse to relay 13|' over a circuit extending from ground by way of contact 4.5,

contact 4|, Contact 44, contact 56, and upper winding of relay 3| to battery. A vbranch ofthe foregoing circuit extendsby way of Ycontact 48 and the upper winding of .the change-over relay 29 to battery. This branch circuit serves to .maintain relay 29 'in operated position during tions of the line relay. Whenthe circuit of .relay 31|I is .closed as described, the relay energizes and prepares a llocking circuit for itself at contact 55. Other results ofthe operation o'f .this .relay will be considered presently.

At'the Vend of the firstinterruption 4o'f the line circuit, the'line relay 21 energizes'and opens the energizing circuit Aofrelay 3|. The 'relay is 'held energized, however, over a circuit extending from the grounded conductor 1| by way of "Contact |41, chain contacts 'including contacts |45 and 15|), contact |`5|, conductor 12,contact'55, lower vwind-ing'of relay l3i), and -upper winding of relay 3| to battery. Relay y'3Q-energizes over ltl-reabove circuit in series with relay 3-| and at contact50 Abreaksthe former-energizingcircuit-of relay 3|,

also preparing -a circuit for deenergizing said relay on 'the-next deen'ergization of' the line relay.

` The line relay has now gone through the first cycle of deenergization and .energizatiom vand :relays 3| and 36 Shavelbeen energized.

Other operationsrhave taken place, due tothe energizati'onofrelay .31. When this relay operates, it closes a circuitrfor the rstfcountin'g relay fIDL'the circuit extending from ground .as previvously traced through the chain contacts |4 |45, and'thence 'by way :of conductor 13, contact 452 of 'relay 3|, .and winding of Vrelay |'0:| 'to .bat-

tery. On energizing, relay locks itself at contact |46, and at contact |34 prepares a circuit for the second counting relay |02. It will be noted also that at contact- |46 relay |0| breaks the initial energizing circuit of relay 34, which now locks up, however, over a circuit extending from the grounded conductor 12, by way of the vupper winding of relay 35, contact 64, andwinding of relay 34 to battery. Relay 35 energizes over the above circuit, locks itself at contact 69, and at contact 68 prepares a circuit for relay 33. Also at Contact 69 relay 35 breaks the initial energizing circuit ofthe change-over vrelay 29, but this relay is maintained in operated position by deenergizations of the line relay, as previously described.

Upon the second interruption in the line circuit, the line relay 21 again deenergizes momentarily and transmits an impulse to relay 29 over the path previously traced. The circuit also continues by Way of contact 50 of relay 30, which is now energized, and by way of contact 53 and the lower winding of relay 3| to battery, also from contact 50 through the upper winding of relay 30 to battery. Relay 3| is differentially Wound and now deenergizes, breaking its locking .circuit at contact 55' and its deenergizing circuit at contact 53. The circuit through the upper Winding of relay 30 maintains this relay energized momentarily until the line relay energizes, whereupon relay 30 deenergizes. At the end of .the second cycle of operation of the line relay, therefore, relays 3| and 30 are both in deenergized position.

When relay 3| deenergizes, it closes a circuit for the second counting relay |02 over a circuit extending from ground by way of contact 41 o-f relay 29, contact 5|, conductor 16, contact |34,

'and winding of relay |02 to battery. On energizing, relay |02 locks itself at contact |45, and prepares a circuit for counting relay |03 (not shown) at contact |38. Relay |02 also breaks the locking circuit of relay |0| at contact |45, and relay |0| yaccordingly deenergizes.

In the foregoing the rst two interruptions of f the line circuit and the first two deenergizations of the line relay 21 have been accounted for.

The second counting relay |02 has been energized. The ensuing deenergizations of the line lrelay which effect the energization of the other counting relays may be described more briefly. It will have been observed that relays 3| and ,30 are energized in response to the first cycle ofoperation of the line relay and are deenergized in response to the second cycle of operation of the line relay. These relays continue to operate in the same manner, energizing on every odd cuit including contact 52, as described, but the remaining counting relays are energized over conductors 14 and 16. The second counting relay |02 energizes over conductor 16, as described.

The third counting relay |03 (not shown but arranged the same as relay |09) energizes over conductor 14. The fourth counting relay |04 .(not shown but arranged the same as relay |02 .or ||0) energizes over conductor 16. Thus the acounting relays are successively energized in response to successive operations of the line relay 21, each counting relay locking itself, breaking vrelay to deenergize.

theV circuit of the preceding relay, and preparing the circuit ofthe succeeding relay.

On the tenth deenergization of the line relay 21, being an even numbered deenergization, relay 3| is deenergized, conductor 16 is grounded, and the tenth counting relay |0 is energized. Relay ||0 locks itself at contact |43 and at thevsarne contact breaks the locking circuit of relay |09, which deenergizes. At contact `|55 relay ||0 prepares a marking circuit for energizing VVthe tenth group relay |20. .r f

The'interruptions of the linecircuit now cease, the tenthV interruption being the last, and the line relay 21 comes to rest in energized position, maintaining the circuit of the release relay 28 closed at contact 4|. Asno more impulses are transmitted to the change-over relay 29, this relay falls back after a brief interval and closes the marking circuit, which extends from ground by Way of contact 45, contact 65, contact 49, contact 54, conductor 11, contact |55 on the tenth counting relay 0, and Winding of the Atenth group relay |20 to battery. Relay |20 energizes over the above circuit, locks itself at contact |49, and connects up the twelve trunks of the tenth group, including the two trunks of this group which are shown in the drawing. Y

When the group relay |20 energizes it also disconnects gro-und from the counting relay chain circuit at contact |49, which breaks the locking circuit of counting relay ||0 and permits this Ground is also disconnected from conductor 12, which breaks the locking circuit of relay 34. Relay 34 accordingly deenergizes, but relay 35 remains energized over its lower winding. When relay 34 falls back, it replaces ground on conductor 12 at contact 65, thus again connecting ground to the counting relay chain circuit including contacts |40, |4|, etc. Since the counting relay ||0 has been deenergized, this chain circuit is now closed, and since relay 35. is in energized position, a circuit is completed for relay 33. The complete circuit may be traced from ground by way of contact 45, contact 65, conductor 12, contact |5|, chain contacts |40-|46, contact 68, and upper Winding of l relay 33 to battery. On energizing, relay 33 locks itself at contact 62.

The function of relay 33 is to start the automatic searching operation, in Which an idle one of the twelve trunks connected'up by the group relay is selected. In energized position, relay 33 connects ground to the test relay 32 at contact 58, prepares circuits for the counting relays at contacts 59 and 60, and at contact 6| closes a circuit for the first counting relay |0|. This circuit includes the grounded chain contacts |40-|45,v conductor 13, contact 6|, and the Winding of relay |0|. On energizing, relay |0| locks itself at Contact |46 and at the same contact breaks the initial energizing circuit of relay 33. This relay remains locked up through its contact 62.

Another result of the energization of relay |0| is the completion of a test circuit extendingfrom ground by Way of contact 58, vWinding of test relay 32, conductor 82, contact |33 of relay 0|, conductor |6|, contact of energized group relay |20, and the test conductor of the first trunk line of the tenth group. This trunk line andthe contacts on relay 20 for connecting it are not shown, but are similar to the two trunk lines and associated contacts that are shown. Y Relay 0 also connects the second counting relay to the above traced test circuit over a path extend.'- i.

ing from conductor 82 by way of contact 51 of test relay 32, contact 59, conductor 16, and con- 'tact |34. Further operations now depend on whether the first trunk of the selected group is idle or busy.

It may be 'assumed that .the trunk lines lead `to `second selectors. These second selectors may be similar to theselector shown lherein, which as previously explained is adapted for use either asa Arst or second selector, The circuit conditions a't the second selectors which render the associated incoming trunk lines busy or idle may vtherefore `be readily understood by reference to the drawings.

In ycase the Aflrst trunk line of the selected l group is busy, the test conductor ISI, which corresponds to test conductor 24, will be grounded due to the energiz'ation of the release relay in the second selector, or due to the busy key corlresponding Yto key BK :being in operated position. .'If the rst trunk line is idle, the test conductor |61- 'will have a battery potential on it. The ycircuit over which the battery potential is derived `may be traced in the selector shown from the `test conductor 24 by way of contact 38, busy key BK, conductor 18, contact |53, conductor 19, contact 69, and lower winding of relay 29 to battery. From this it will be understood that the lfirst selector `whose operation is being described :is searching for a trunk line the test conductor of which has a battery potential on it, ythisbattery potential denoting an idle trunk line.

It ymay 'be assumed 'that the first trunk line of .the selected group is busy, in which case there will bea ground potential on test conductor 16|,

as previously explained. The test conductor being grounded, the test relay 32 will be prevented -from energizing, and the second counting relay |02 will be Venergized over the circuit previously traced, extending from ground on the test conductor |6l, and by way of conductors 82 and 16 to relay |02. When counting relay |32 energizes, .it `locks itself at contact |45 and at the same contact 'opens the locking circuit of counting relay HH., which deenergizes. Relay |32 also connects iup -theitest'conductcr |62 of the second Itrunk line at contact |36 and at contacts |31 and |38 closes a circuit for energizing the third counting relay |03 in case the second trunk line liswbusy. The third counting relay is not shown but is arranged thesame as relay |09.

Assuming lthat 'the second trunk line is busy .and that the test conductor |62 is grounded, the third ycounting relay will be energized over a circuit which extends from the grounded test Iconductor |-62by way of contact |36, conductor ,v8-2, contacts 51 :and 59, conductor v16, contact |34, contact 13'1, `conductor 15, contact 60, conductor 14,-contact |38, and winding of the third counting relay to battery. On energizing, the third'counting relay locks itself, breaks the locking circuitof the second counting relay, and prepares a circuit for the fourth counting relay. The 'circuit arrangements at the third counting relay are the same as those at first and ninth counting relays, while the fourth counting relay is arranged the same as the second and tenth counting relays.

It will be clear from the foregoing that the test relay 32 cannot energize so long as the counting relays connect up test conductors of busy trunk lines. The counting relays, on the other hand, energize in succession in the manner .described until the test conductor of an idle .trunk line is connected up. It will be assumed that the eleventh trunk line is the rst. `idle trunk line, and accordingly relay will be energized in due course, following the energization of the preceding relays in the manner expIained.

On energizing, relay locks itself at contact |42, vat the same time breaking the locking circuit of counting relay IIIl. The latter relay therefore deenergizes. Relay also connects up the test conductor |1| of the eleventh trunk line at Contact |13, and at contact |12 extends the test conductor through to relay ||2. Relay l2, however, is not energized, due to the absence of ground potential on test conductor |1|, and to the operation of the test relay 32.

When relay energizes, two parallel circuits are established for the test relay. One of these circuits extends from ground by way of contact 58, winding of `test relay 32, contacts 51 and 59,

conductor 16, contacts |34, |31, etc., including contact |12, and winding of relay ||2 to battery. The other circuit extends from ground by Way of contact 58, winding of test relay '32, conductor 82, contact |13, test conductor |1|, and contact of group relay |20 to test. conductor |32, and thence to battery through the lower winding of the change-over relay in the second selector. As previously explained, the battery potential indicative of the idle condition of the trunk line is ,placed on the test conductor through the winding of the change-over relay. The current flow through the test relay and over the Ilast described circuit is suilicient to operate the test relay, the energization of the relay being expedited somewhat at the start by the current flow over the `first described circuit extending back over conductor 15 to relay |.|2. The circuit through relay |=|2 is broken at contact 51 as soon as relay .32 has partially operated'and consequently relay 1| |.2 cannot energize.

The test relay 32 also closes a circuit for the switching relay 2S, extending from ground by way way of contact |52, conductor- -85, contact 53, and winding of relay 28 to battery. On energizing, relay 23 locks itself lat contact 39 to the grounded test conductor 24, Other results of the energization of relay 2S will be described.

At contactl 3B, relay 26 disconnects conductor 1D from the test conductor 24 and thus removes ground from conductor 1|), which breaks the locking circuits of relays 33 and 35. These two relays accordingly deenergize. Also at contact 33 relay 26 extends the incoming test conductor .24 to conductor 82 and thence over conductor vtrunk conductors 22 and 23 from the windings of #the line relay 21 and extends them by way of conductors I83 and 8|, contacts `66 and 61, conductors Sil v'and 8|', contacts |14 and |15, conductors |16 and |11, contacts of group relay |20, and line conductors |30 and |3| of the selected idle trunk to the line relay of the second selector in which such trunk terminates.

The line and release relays in the second selector are accordingly energized and the latter relay places ground on the test conductor |32. Thus ground potential is extended back over conductors |32, |1.|and82 'to the test conductor 24 to maintain this conductor grounded and to hold the switching relay 2B energized. The line relay 21 deenergizes when it is disconnected and the release relay deenergizes an instant later. 'Ihe falling back of the latter relay is without effect at this time, for the test conductor 24 has'been grounded at the second selector and the holding conductor 25 has been directly grounded at relay 26, all as previously described.

The operation of the selector has now been completed. The tenth group of trunks has been selected bythe operation of the counting relays in response to the dialling of the digit and the eleventh trunk in such group has been selected and connected with automatically. 'I'he connection is maintained by relays 26, and |20. When the subscriber dials the remaining digits of the called number, the connectionis further extended to the called subscribers line in known manner, through the operation of the second selector which has been connected with one or more additional selectors if the size of the system is such as to require their use, and a connector. When the calling subscriber. hangs up his receiver, the connection is released. The replacement of the receiver opens the bridgeacross the line, which brings about the deenergization of the line and release relays, usually located at the connector, which control the maintenance of the connection. The deenergization of the release relay removes ground from the test circuit, extending back through the selector or selectors and permits them to restore to normal. `At the selector shown herein, the removal of ground l from test conductor|32 breaks the circuit ofy the switching relay 25, which deenergizes and removes ground from conductors 'H and`12, permitting relays |20 and I to'deenergize. 'Ihe selector is thus restored to normal, Relay 26 alsoA removes ground from the holding conductor 25, which permits relays 20 and 2| to restore. The removal of ground from test conductor 24 deenergizes the subscribers cut-off relay and removes the busy potential from the test conductor |4, which makes the line of station A accessible to incoming calls. Thus all the equipment, the operation of which has been described, is restored to normal condition and is ready for use inestablishing other connections.

Certain features of the operation of the` selector which it was not convenient to describe before may now be discussed briefly. One of these features has to do with the operation' of testing for idle trunks. It has been explained that busy trunks are characterized by having a ground potential on their test conductors, Whereas the test conductors of idle trunks have batterypotentials on them, and it has been further explainedA that the ground potentials on the test conductors of busy trunk lines operate the counting relays while the battery potential on the i'lrst idle trunk operates the test relay. It may now be pointed out that the presence of a ground potential on the test conductor of a trunk line is not necessary in order to eie'ct the continuance of the hunting operation, which will continue until a trunk line having battery potential on its test conductor is found, trunk lines the test conductors of which have no potential on them at all being passed by as well as those having grounded test conductors. f

In order to explain the foregoing, it may be assumed that the operation of testing for an idle trunk line has been started and that4 relay |0| relay, through which battery potential isvplaced has" energized, connecting up thetest conductor |6|l of the first trunk line. It may be further assumed that conductor ISI has neither a ground potential nor a battery potential on it. This condition may be due to trouble of some kind, such as a dirty contact or a broken connection. Under these circumstances the test relay 32 cannot energize over test conductor ll, due to the absence of battery potential thereon, nor can the relay |02 energize over said test conductor, due to the absence of ground potential. Relay |02, however, energizes over another circuit extending from ground by way of Contact 58, Windingr of test relay 32, contacts 5l'l and 59, conductor 15, contact |34, and windingof relay |02 to battery. Relay |02 is of relatively Ahigh resistance, and relay 32 cannot energize in series with relay |02, or any of the other counting relays. Accordingly, the hunting operation proceeds, vthe counting relays being energized normally by ground potential on the test conductors ofbusy trunk lines, but energizing in series with vthe test `relay in case trunk lines are tested which have no potential on their test conductors. f

In view of the foregoing, it will' be understood that the test relay 32 is a so-called marginal relay, of relatively low resistance, which is-incapable of energizing in series wtih a high resistance counting relay, but is adapted to energize in series with the lower winding of a change-over on the test conductor of a trunk line to indicate theidle conditionthereof. The lower-windings of the change-overl relays are of lower resistance than the windings of thecounting relays. 'Ihe resistance of the change-over relays is, however, so proportioned to the operating characteristics of the test relays that two test relays in parallel cannot energize in series with a change-over relay, which prevents two selectors which may happen to be searching at the same time from selecting the same idle trunk.

It will have been noted-that the conductors and8| extend direct to contacts of the even numbered counting relays, whereas the odd numbered counting relays are reached by way of the branch conductors 80 and 8|. Thelatter conductors are normally connected to conductors 80 and 8|, respectively, but are disconnected therefrom by relay 35, which is energized when dialling begins and remains energized until the automatic trunk hunting operation is completed. The purpose of thisv arrangement is to prevent the momentary connecting together of adjacent trunk lines during the hunting operation of the selector. Relay |02 is energized,for example, before relay |0| is deenergized, and if conductors 80 and 8| were connected to contacts of both relays I 0| and |02the rst and second trunk lines of the group selected by the energized group relay would be momentarily connected together. The use of separate pairs of conductors extending to the connecting contacts of the odd and even counting relays, which are not connected together until relay 35 deenergizes .after-the trunk hunting operation is completed, avoids the disturbance which would otherwise take place on adjacent busy trunk lines when tested by a selector in search of an idle trunk line.

For a similar reason two separate marking conductors such as TI are provided, and are`con= nected up alternately by relay 3|. The marking contacts of adjacent counting relays therefore do not have a common multiple, and the vdanger of operating additional group Vrelays duringthe separate conductors leading from relay 3| to the marking contacts of the odd and even counting relays prevents such false operation of the group relays.

The operation and function of the overow relay |`|3 may now be explained. In case all the trunk lines of a selected group are found to be busy, all of the relays IBI to ||2, inclusive, will be energized in succession during the hunting operation and following the energization of the lastl relay I|2 the overflow relay ||3 will be energized in an obvious manner, the circuit being similar to the circuitsover which relays |09` and |I`| are energized. On energizing, relay ||3' locks itself at contact |53, and at the same point breaks the locking circuits of relays 33 and 35', which accordingly deenergize. At contact |45, relay ||3 breaks the locking circuit of relay ||2, and this relay deenergizes. At contact |41 relay ||3 places direct ground on the locking circuit of the energized group relay, whichv may be assumed to berelay |20. Finally, at Contact |54, relay ||3' connects a source of busy signalling current to the calling line and the calling subscriber is given the busy signal.

On hearing the busy tone, the calling subscriber will hangup hisreceiver, whereupon the line relay 21 is deenergized, followed an instant later by the deenergization of the release relay 281. A circuit for operating the everow register for the tenth group of trunk lines is thereupon established, said circuit extending from ground by way of contacts 4U, 4|, and 44, conductor 95, contact |48, lower contact or group relay and conductor |80 to the overiiow register (not shown), and thence to battery. At the same time that the above circuit is completed, relay 28 removes ground from the test conductor 24, also from conductor 10, and breaks the locking circuit of relay M3. This relay is slow to cleenergize, however, and remains in operated position long enough for the overflow reg-- ister to be actuated. When relay ||3 finally resto-res, the locking circuit of the group relay |20 is broken at contact |41 and the group relay restores also.

` The circuits are so arranged that the overiiow relay ||3 is also operated in case the digit 1 is dialled, accidentally or otherwise. Since the first trunk group is not assigned at the first selectors, no telephone numbers start with the digit 1, and hence the receipt of a single isolated impulse or line circuit interruption at a first selector must be. due to the calling subscriber dialling a wrong number, or to an accidental opening of the line circuit such as mayv be produced by careless removal of the receiver. Such accidental interruptions of the line circuit are known as preliminary impulses.

Assuming that the `selector shown herein has beenv taken for useI as previously described, if a single interruption is produced in the line circuit, the line relay 21 is momentarily deenergized once and relays 3| and 30 are energized. Relay 3| closes a circuit for the rst counting relay Iil, which energizes and locks itself, at the same time opening the initial energizing circuit of relay 34. Relay 35 now energizes in series with relay 34, locks itself to conductor 19, and breaks the initial energizing circuit of the change-over relay 29. The change-over relay is energized over its upper winding during the time that the line relay 21 is deenergized, but falls back shortly after the line relay resumes its energized position. On restoring, relay 29 closes a marking circuit extending` from ground by way of Contact 45, contact 65, contact 49, contact 54, Contact |35, and winding of the overflow relay I3 to battery.

When the overflow relay I3 energizes over the foregoing circuit it locks itself atl contact |53. At contact |5I, relay I|3 removes ground from conductor 12', which causes relay 34 to deenergize, as well as relays 34] and 3|. Relay 35 also de- I energizes, due to the breaking of its locking circuit at contact |53 of relay H3. At contact |40, relay V| |13 breaks the locking circuit of relay |0|, whichv d'eenergizes. Thus only the line and release relays and the overflow relay remain in energized position. At contact |54 the overflow relay connects the busy tone circuit to the calling line, and the calling subscriber is given the busy signal. When the calling subscriber replaces his receiver, the line and release relays are restored,

. and the connection to the selector is released as previously described. The removal of ground from the conductor 10 breaks the locking circuit of` the overow relay, which accordingly deenergizes.

The invention having been described, that which is believed to be new and for which the protection of Letters Patent is desired will be pointed out in the appended claims.

' What is claimed is:

1. In an automatic selector switch, means including a series of counting relays directively controlled in accordance with a digit of a called number for selecting any one of a plurality of groups of trunk lines, and means eiective automatically responsive Vto the completion of the group selection for reoperating said counting relays to search for an idletrunk line in the selected group.

2. In an automatic switch of the relay type, a plurality of group relays each adapted to establish connections simultaneously with'a group of trunk lines, means including a chain of counting relays directively controlled in accordance with a digit in a called number for selecting and energizing one of said group relays, thereby selecting the associated group of trunk lines, and means for operating said counting relays automatically to search for and connect with an idle trunk line.

3. In an automatic switch of the relay type, a plurality of group relays each adapted to establish connections with a plurality of trunk lines, a chain of counting relays directively controlled in accordance with a variable series of digit impulses for selecting one of said group relays, means for automatically energizing the selected group relay at the end of said series of impulses, and means for reoperating said counting` relays automatically to select an idle trunk in the group connected with by the energized group relay.

4. In an automatic switch of the relay type, a pluralityv of group relays each adapted to establish connections with a plurality of trunk lines, a'chain of counting relays directively controlled in accordance with a variable series of digit impulses for selecting one of said group relays,

means responsive to the termination of said series of impulses for energizing the selected group relay, means responsive to the energization of the selected group relay for starting the automatic operation of said counting relays to search for an idle trunk line in the group connected with by the energized group relay, and circuits including the test conductors of busy trunk lines for continuing the automatic operation of said counting relays until an idle trunk line is found.

5. In an automatic switch adapted to perform directive and automatic selective operations, a line relay, a test relay, a series of counting relays, means for operating said counting relays under the control of said line relay during the directive operation of said switch, and means for operating said counting relays under the control of said test relay during the automatic operation of said switch.

6. In a relay'type selector switch, trunk group connecting relays, counting relays individual to said connecting relays, respectively, a circuit for each connecting relay including contacts on its associated counting relay, sets of trunk connecting contacts on each of said connecting relays, a trunk incoming to said selector switch, and contacts on said counting relays for extending said incoming trunk to any contact set on any connecting relay.

7. In an automatic-selector switch,'means including a series of counting relays directively controlled in accordance with a digit of a called number to select any one of a plurality of groups of trunk lines, one or more of said trunk groups comprising a number of trunk lines which is greater than the number of counting relays, additional relays equal in number to the difierence between the number of counting relays and the number of trunk lines in the largest group, and means responsive to the completion of a group selecting operation for automatically operating said counting relays and said additional relays to select an idle trunkv line in the selected group.

8. In a relay type selector switch, an incoming trunk, a plurality of groups of outgoing trunks, a series of counting relays controlled over said incoming trunk to select a group of outgoing trunks, a larger series of relays including the relays of said rst series, means for automatically and successively operating the relays of said last mentioned series to test the trunk lines of the selected group in rotation until an idle trunk is found, and means including'contactson the last operated relay for connecting said incoming trunk to the selected idle outgoing trunk,

9. In a selector switch, a group relay havingA contacts for simultaneously connecting up a group of trunk lines, a series of vcounting relays greater in number by one than the number of trunk lines in said group, means controlled over a calling line for operating a predetermined number of said counting relays to energize said group relay, means for automatically operating a variable number of said counting relays to search for an idle trunk line in said group, said last means being eiTective to operate all of said counting relays in case all of said trunk lines are busy, and means including the last counting relay for transmitting a busy signal over the calling line 10. In a relay type selector of group relays, each adapted to close connections to a group of trunk lines, a plurality of counting relays operable to select a desired group switch, a plurality of trunks by energizing onehofsaid group relays and also operable to select an idletrunk in the selected group, an over'ow relay and means for controllable over a -calling line for performing a directive operationto select one of said groups v of trunk lines, meansvfor operating saidV counting relays to perform an automatic searching operation for an idle trunk in the selected group, means including an overflow relay for connecting a busy signalling device tothe calling line, and means for operating said overiiow relay in response to a particular directive operation and also in response to an unsuccessful searching operation.

12. In a relay type selector switch, a series of counting relays, means for` utilizingsaid series of relays for performing directive and automatic selective operations, two separate control conductors over which the odd andfeven numbered counting relays are operated, respectively, during the directive operation of 'the switch, a common operating conductor yand means for connecting it to one of said control conductors during the automatic operation of the switch, and contacts on the relays operated over such control conductor which are rendered effective during the automatic operation of the switch for connecting the said control conductors together.

13. In a relay type selector having access to a group of trunk lines, a series of relays adapted to hunt for an idle trunk` in said group, a test circuit for successively energizing said relays and comprising two sections, contacts on each of said relays for extending one section of said test circuit to the next adjacent relay, other contacts on said relays for extending the other section of said test circuit tothe test 'conductors of said trunk lines one after the other, anda test relay connected to the junction of said sections.

14. In a relay type selector switch having access to a group of trunk lines, a trunk testing arrangement comprising a test relay, a series of connecting relays for closing connections to the.

test conductors vof said trunk lines in succession, and circuit arrangementsk such that said test relay isl energized by potential of one polarity on any one of said test conductors, whereas said connecting relays are energized by potential oi"y the opposite polarity on said test conductors, respectively, or by current flow through said test relay in the event that a connection is closed to a test conductor on which no potential is present.

15. In a relay type selector, group relays, a series of counting relays, means controlled over a calling line for directively operating said counting relays to select one of said group relays, means including a chain circuit-extending through contacts of said counting relays whereby each relay on energizing locks itself and unlocks the preceding relay, means for energizing the selected group relay, means including a chain Vcircuit extending through contacts of al1 said group relays for locking any group relay when energized, and connections for supplying current to the counting relay chain circuit through the group relay chain circuit, whereby the energization of any group relay will deenergize the last operated counting relay.

16. In a relay type selector switch, a plurality a plurality of whereby the group relay chain circuit is broken,

means for automatically operating said counting relays to select an idle trunk in the group associated with the selected group relay, and means responsive to the breaking of the group relay chain circuit for supplying current to the saidv counting relay chain circuit during the automatic operation of the switch over a path independent vof said group relay chain circuit.

17. In a relay type selector switch, group relays each having a plurality of sets of trunk connecting contacts, a series of counting relays, an incoming trunk having twoV branches, one branch extending to the odd numbered counting relays and the other extending to the even numberedcounting relays, contacts on the counting relays for extending said branches to contact sets on said group relays, means for successively operating -said counting relays, and a relay for maintaining said branches disconnected from each other whi-le said coun-ting relays are being operated.

18. In a relay typeselector switch, group relays, a series of counting relays, a control relay energized after each odd selector controlling impulse and deenergized after each even selector controlling impulse, circuits over which said control relay successively operates said counting relays, a. marking conductor having two branches, contacts on said control relay for alternately connecting said branches to said marking conductor, contacts on the odd numbered counting relays for extendingone branch tothe odd numbered group relays, and contacts on the even numbered counting relays for extending the other branch to the even numbered group relays.

- 19. In a relay type selector switch, a series of counting relays, means for utilizing said relays to perform a directive selecting operation and subseq-uently an automatic searching operation, a chai-n circuit extending` through serially related contacts on saidrelays which` is maintained open at successive relays while said relays are performing said directive selecting operation, means for deenergizing any relay remaining operated at the end of said directive selecting operation, thereby closing said chain circuit, and a relay energized over said chain circuit responsive to such closure for starting said automatic s earching operation.

20. In a relay type selector switch, a series of counting relays, a chain circuit extending through serially related contacts on said relays, means for successively operating said relays in accordance with a digit in a called number, said chain circuit being broken by the rst operated relay, and an off normal relay-energized responsive toy the breaking of said chain circuit.

21. In a switching system, an automatic switch of the relay type, groups of lines accessible to said' switch, group relays assigned respectively to saidgroups of lines, local. line conductors in said switch, a chain of counting relays directively controlled in accordance with a variable series -of digit impulses for selecting and operating any one of said group relays, each group relay adapted when operated to connect` said localv line conductors respectively with the lines of the group to which such group relay is assigned, said counting relays being adapted to select and connect with any one of said local conductors, and means effective after group connection has been made for variably repositioning saidcounting relays to eiect connection by way of any one of said localconductors with the corresponding line in the connected group.

22. In a switching system, an automatic switch of the relay type, groups of lines accessible thereto, a separate group relay in said switch for eachof said groups of lines., a series of counting relays and means for directively operating them to effect the operation of any one of said group relays, sai-d group relays being adapted when operated to make connections tothe respective lines in the associated group, and means ,controlledthrough said connections for variably repositioning said counting relays in accordance with the respective conditions of the selected lines.

23. In a switching system, an automatic switch of the relay type, groups of lines accessible thereto, a separate group relay in said switch for eachof said groups of lines, a series of counting relays and means for vdirectively operating them to effect the operation of any one of said group relays, said group relays being adapted when oper-l ated to make connections to the respective lines in the associated group, means controlled through said connections for Variably repositioning said counting relays in accordance with the respective conditions of the selected lines, said counting relays being adapted when repositioned to extend the one of said connections corresponding to the repositioning effected.

24. In a switching system, an automatic switch of the relay type, groups of lines accessible to said switch, group relays in said switch corresponding respectively to said groups of lines, individual relays in sai-d switch corresponding respectively to the individual lines in a group, means for directively operating the individual relays successively to select and operate any one of said group relays to select a group of lines, and means for subsequently operating any one of saidy individual relays to effect connection with the corresponding line in the selected group.

NORMAN H. SAUNDERS. 

